One of the problems which is repeatedly encountered concerns the extraction, purification, concentration and conservation of biological material for the purpose of subsequent use.
One of the protein purification methods used is purification by precipitation using precipitating agents, such as ammonium sulfate or poly(acrylic acids) (H. Morawetz and W. L. Hughes, J. Phys. Chem., 56, 64-69 (1952)).
Another method relates to the extraction of biological material using colloidal suspensions. Mention may be made of patent application WO-A-98/01482 by Krupey, which describes extraction of proteins in an aqueous medium using colloids based on crosslinked maleic anhydride copolymers. After complexation of the proteins on the colloids, the complexes are extracted from the medium by centrifugation. Such a method has the drawback of requiring a relatively delicate centrifugation step and involving considerable and expensive equipment which, in addition, is not always readily accessible.
A possible solution is to use magnetic iron oxide colloids, as described by V C Rao et al. (Appl. Environ. Microbiol., 1981, September, 42(3): 421-426). However, it is known that iron oxides are incompatible with techniques for enzymatically amplifying nucleic acids since they inhibit the enzymes.
To solve this problem, it has been proposed (patent application WO-A-99/35500) to cover magnetic particles with a cationic or anionic hydrophilic polymer, which masks the iron oxides and which thus makes it possible to lift the inhibition of the enzymatic amplification reaction, after a step of extraction of the nucleic acids. This polymer is a heat-sensitive polymer which, when it is heated to a temperature greater than 32° C., becomes hydrophobic and can attach proteins via hydrophobic interactions. However, hydrophobic interactions are denaturing for a large number of proteins.